Dependence of tissue optical properties on solute-induced changes in refractive index and osmolarity

Abstract

Additions of a solute/carbohydrate in tissue affect the size of tissue cells and the refractive indexes of the extra-and intracellular fluids, and thus the overall tissue scattering properties. We use both the Rayleigh-Gans and Mie theory approximation in calculating effects of the osmolarity and refractive indexes on the reduced scattering coefficient of tissue, and employ photon diffusion theory to associate the reduced scattering coefficient to the mean optical path length. The calculations show that changes of scattering in tissue depend not only on the change in extracellular refractive index but also on the change in osmolarity, and thus on the change in cell size and volume fraction. Experimentally, we have utilized time-domain and frequencydomain NIR techniques to measure the changes of optical properties caused by an addition of a solute in tissue models and in perfused rat livers. The temperature-dependent path length measurement of the perfused liver confirms the dependence of tissue scattering on the tissue cell size. The results obtained from the liver with three kinds of carbohydrate perfusion display different scattering aspects and can be well explained by changes in cell size and in extracellular as well as intracellular refractive indexes. The consistency between the theoretical and experimental results confirms the dependence of optical properties in (liver) tissue on both tissue osmolarity and relative refractive indexes between the extracellular and intracellular compartments. This study suggests that the NIR technique is a novel and useful tool for noninvasive, physiological monitoring.

Development of an Optical Tissue Clearing Laser Probe System

“…3 demonstrates that decreasing the tissue temperature resulted in decreasing the µ's and, therefore, increasing the PI and TI which means enhancement of photon density in the dermis. As described in previous studies, such results may be caused by the modification of collagen fiber structure, degradation of cellular components, and change of the refractive index of intercellular fluid [15][16][17][18][19][20].…”

“…The LBP remarkably increased when compared to control. Skin dehydration and collagen dissociation may cause the reduction of light scattering by minimizing refractive index mismatching [15][16][17]. Recently, Yu et al [19] reported that the dehydration induced by an optical clearing agent is a prominent mechanism for improving tissue optical transmittance.…”

“…Since Tuchin et al [13] first reported an OTC method using chemical agents, numerous investigations have been performed to understand the OTC mechanism, such as skin dehydration, partial replacement of the interstitial fluid by the immersion substance, structural modification or dissociation of collagen, and a combination of the two [13][14][15][16][17]. Rylander et al [18] and Yu et al [19] that skin dehydration is the prominent mechanism of OTC and Yeh et al [20] suggested that the reversible change of both collagen structure and size can affect OTC.…”

Glucose diffusion in tissue engineering membranes and scaffolds

“…This method presents some advantages over others due to its capability to measure concentration in situ without interrupting the process as well as the simple post processing work thereafter. As such, the method has been used since in the early 1990s up until recently (Maier et al 1994, Chance et al 1995, Liu et al 1996, Tuchin et al 1997, Wang 2000, Vargas et al 2001, Yao et al 2002, Bashkatov et al 2003, Zhang et al 2013a,b, Trichet et al 2014, Ullah et al 2014, Pleitez et al 2015.…”

“…Numerous glucose diffusion studies have been reported for a vast number of applications ranging from TE (Hannoun and Stephanopoulos 1986, Weng et al 2005, Rong et al 2006, Papenburg et al 2007, Jin et al 2010, Podichetty et al 2014, diabetes management (Maier et al 1994, Wang and Musameh 2003, Boss et al 2012, modern laser medicine (Chance et al 1995, Liu et al 1996, Tuchin et al 1997, Wang 2000, Vargas et al 2001, Yao et al 2002, Bashkatov et al 2003, pharmaceutics (Andersson et al 1997), chemical engineering, filtration (Yaroshchuk et al 2011, Adams et al 2013), oil and fat industry (Miyagi et al 2012), and water desalination (Lonsdale et al 1965, Sherwood et al 1967. A review of these studies suggests that a number of different techniques could be applied to measure glucose concentration or diffusivity as discussed below.…”